A metal plate such as an aluminum plate has been used as a support of a printing plate material. However, recently, a printing plate material employing as a support a polyester film sheet has been developed which is easy to handle and carry (see for example, Japanese Patent O.P.I. Publication Nos. 4-261539, 5-257287 and 2000-258899). In the off-set printing press widely used in the printing industry a gripping system (see for example, Japanese Patent O.P.I. Publication No. 3-176152) is well known which folds a printing plate at a specific angle and mounts the printing plate on a plate cylinder of the printing press. This system is designed so as to meet properties of a printing plate employing as a support a metal plate such as an aluminum plate. Accordingly, when the edge portion of a printing plate employing as the support a polyester film sheet being folded at a specific angle, the printing plate is mounted on such a cylinder and printing is carried out, the printing plate has the problem of poor dimensional stability, which results in “out of position”, “out of registration” or “out of color registration” during printing. Further, the printing plate has problems in poor ink receptivity at the beginning of printing and poor printing durability.